Abstract
Although the temperature response of soil respiration (Rs) has been studied extensively, several issues remain unresolved, including hysteresis in the Rs–temperature relationship and differences in the long- vs. short-term Rs sensitivity to temperature. Progress on these issues will contribute to reduced uncertainties in carbon cycle modeling. We monitored soil CO2 efflux with an automated chamber system in a Pinus tabulaeformis plantation near Beijing throughout 2011. Soil temperature at 10-cm depth (Ts) exerted a strong control over Rs, with the annual temperature sensitivity (Q 10) and basal rate at 10°C (Rs 10) being 2.76 and 1.40 µmol m−2 s−1, respectively. Both Rs and short-term (i.e., daily) estimates of Rs 10 showed pronounced seasonal hysteresis with respect to Ts, with the efflux in the second half of the year being larger than that early in the season for a given temperature. The hysteresis may be associated with the confounding effects of microbial population dynamics and/or litter input. As a result, all of the applied regression models failed to yield unbiased estimates of Rs over the entire annual cycle. Lags between Rs and Ts were observed at the diel scale in the early and late growing season, but not in summer. The seasonality in these lags may be due to the use of a single Ts measurement depth, which failed to represent seasonal changes in the depth of CO2 production. Daily estimates of Q 10 averaged 2.04, smaller than the value obtained from the seasonal relationship. In addition, daily Q 10 decreased with increasing Ts, which may contribute feedback to the climate system under global warming scenarios. The use of a fixed, universal Q 10 is considered adequate when modeling annual carbon budgets across large spatial extents. In contrast, a seasonally-varying, environmentally-controlled Q 10 should be used when short-term accuracy is required.
Highlights
A global effort is underway to mitigate anthropogenic climate change through afforestation/reforestation, in hope of sequestering carbon in plantation ecosystems
Pulse dynamics in volumetric water content (VWC) were obvious from May through
Cross-correlation analyses revealed that, the correlation between daily mean Rs and Ts was highest at zero lag for all locations, the correlation coefficient was strongly asymmetric about the zero lag, with negative lags (Rs lagging Ts) reducing the correlation coefficient much more rapidly than positive lags
Summary
A global effort is underway to mitigate anthropogenic climate change through afforestation/reforestation, in hope of sequestering carbon in plantation ecosystems. Understanding the environmental controls on carbon dynamics in new plantations is crucial for projecting future global carbon budget and climate scenarios, and could aid in assessing the effectiveness of carbonoriented management practices in forestry. Aside from its large quantity, Rs is exponentially related to soil temperature (Ts) in most ecosystems 3,4]. Even subtle changes in climate (e.g., rising atmospheric temperature) could trigger significant changes in Rs, markedly altering ecosystem carbon budgets. Despite the large body of literature on the interactions between Rs and climate change, the response of soil carbon processes to climatic factors (e.g., Ts and soil moisture) is not well-known and remains a source of uncertainty in ecosystem carbon modeling 6,7]
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